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[Launchpad Bug Tracker <1335311@xxxxxxxxxxxxxxxxxx>]

** Branch linked: lp:ubuntu/utopic-proposed/mir

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https://bugs.launchpad.net/bugs/1335311

Title:
  MultiThreadedCompositor deadlocks

Status in Mir:
  Fix Committed
Status in Mir 0.4 series:
  Fix Released
Status in “mir” package in Ubuntu:
  Fix Released

Bug description:
  The easiest way to reproduce is to use double buffering -
  src/server/compositor/buffer_stream_factory.cpp:

  auto switching_bundle = std::make_shared<mc::BufferQueue>(3, gralloc,
  buffer_properties, *policy_factory);

  auto switching_bundle = std::make_shared<mc::BufferQueue>(2, gralloc,
  buffer_properties, *policy_factory);

  Then:

  mir_demo_server_shell --display-config=sidebyside
  mir_demo_client_egltriangle -n

  In the shell: ALT+Ctrl+<arrow keys> to change orientation which will
  restart the compositor.

  It's a race between 3 threads:

  Thread A owns SceneObserver::mutex, responding to a frame_posted
  notification, waiting to acquire CompositingFunctor::run_mutex
  (MultiThreadedCompositor::schedule_compositing)

  Thread B owns CompositingFunctor::run_mutex and it's waiting to
  acquire RenderingTracker::guard (due to
  display_buffer_compositor_factory->create_compositor_for(buffer);)

  Thread C executing display_buffer_compositor->composite(), owns
  RenderingTracker::guard and its waiting to acquire
  SceneObserver::mutex

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